Endophyte Effects on Photosynthesis and Water Use of Plant Hosts: A Meta-Analysis

Endophytes – bacteria, fungi, and yeast living inside plants – can provide multiple benefits such as growth promotion and stress tolerance for their host to be successful in diverse environments. In this chapter, we review current literature to provide a meta-analysis on how the benefits conferred by endophytes are modulated through photosynthesis and water relations of the host plants. A total of 30 articles collectively demonstrated that endophyte inoculations led to photosynthetic improvements characterized by an increase in chlorophyll content, photochemical efficiency, or net CO2 assimilation rate. An increase in leaf N content by either biological N fixation or N assimilation and translocation facilitated by endophytes, in part, accounted for these improvements. In addition, water use efficiency (WUE) of the host plants was enhanced by endophytes but this response was highly variable among studies conducted under different environmental conditions. An efficient osmoregulation and stomatal control modulated by endophytes are among the potential mechanisms that explain the improvements in WUE. We suggest that future studies need to consider the cost-benefit perspective of the plant-endophyte associations in terms of carbon, water, and nitrogen balances.